Photovoltaic devices are known in the art (e.g., see U.S. Pat. Nos. 6,784,361, 6,288,325, 6,613,603 and 6,123,824, the disclosures of which are hereby incorporated herein by reference). Amorphous silicon (a-Si) and CdTe type (including CdS/CdTe) photovoltaic devices, for example, each include a front contact or electrode.
The high temperatures sometimes necessary for depositing the semiconductor may cause sodium effusion and/or diffusion from the glass to the semiconductor. Moreover, some transparent conductive oxide materials that exhibit favorable properties when used as a front contact may have an index of refraction higher than that of the glass, and thus may exhibit reflectance at the surface of the glass. Further, in certain instances, some transparent conductive oxide materials may be cost-prohibitive.
Thus, it will be appreciated that there exists a need in the art for a more efficient and/or improved photovoltaic device, and/or a front electrode structure therefor. It also will be appreciated that there is a need in the art for a technique for making or forming a TCO electrode structure.
Certain example embodiments of this invention relate to a buffer layer provided in connection with a front electrode in a photovoltaic device or the like. In certain example embodiments, a front electrode structure includes a cadmium stannate-based transparent conductive oxide (TCO) layer and/or a cadmium stannate-based buffer layer that are provided between the front glass substrate and the semiconductor absorber film in a photovoltaic device. The cadmium stannate-based TCO and/or buffer layer(s) may be deposited via sputtering or the like, and may or may not be doped in certain example instances. In an example context of CdS/CdTe photovoltaic devices, for example, the cadmium stannate-based layer(s) is/are advantageous that they may (a) provide for high transmittance into semiconductors such as CdS and/or CdTe; (b) have low absorption, thus further increasing the transmittance; (c) allow the coating to have a high figure of merit; and/or (d) provide good durability when used with a sodium barrier layer, e.g., in terms of being able to better withstand the migration of sodium through the glass due to the elevated temperatures during CdS/CdTe deposition and/or processing.
In certain example embodiments, the electrode structure (including the electrode and the buffer layer) may be used as any suitable electrode structure in any suitable electronic device, such as a photovoltaic device, electro-optical device, or the like. In certain example embodiments of this invention, the electrode structure may have a sheet resistance (Rs) of from about 7-50 ohms/square, more preferably from about 10-25 ohms/square, and most preferably from about 10-15 ohms/square using a reference example non-limiting thickness of from about 1,000 to 2,000 angstroms.
In certain example embodiments of this invention, there is provided photovoltaic device comprising: a front glass substrate and a plurality of thin film layer disposed thereon, the thin film layers comprising, in order moving outwardly from the front glass substrate: at least one index-matching layer, a transparent conductive oxide (TCO) layer comprising CdSnOx, a buffer layer comprising CdSnOx, wherein the buffer layer comprising CdSnOx has a resistivity higher than a resistivity of the TCO layer comprising CdSnOx, a semiconductor film comprising CdTe and/or CdS, and a rear contact layer, and a rear glass substrate.
In certain example embodiments of this invention, there is provided a photovoltaic device, the photovoltaic device comprising: a front glass substrate and a plurality of thin film layer disposed thereon, the thin film layers comprising, in order moving outwardly from the front glass substrate: a sodium barrier layer; a plurality of index matching layers including at least a high-index titanium oxide inclusive layer and a low index silicon-inclusive layer; a transparent conductive oxide (TCO) layer comprising CdSnOx; a buffer layer comprising CdSnOx, wherein the buffer layer has a higher resistivity than a resistivity of the TCO layer comprising CdSnOx; and a semiconductor film comprising CdS and/or CdTe.
In certain example embodiments of this invention, there is provided a method of making a photovoltaic device, the method comprising: providing a front glass substrate; sputter-depositing a barrier layer directly on the front glass substrate; sputter-depositing at least one index matching layer onto the glass substrate, over and contacting the barrier layer; sputter-depositing a transparent conductive oxide (TCO) layer comprising CdSnOx and having a resistivity of no greater than 0.4 mohm-cm and a refractive index from about 1.8 to 2.2, directly or indirectly, on the at least one index matching layer; and sputter-depositing a buffer layer comprising CdSnOx directly on the TCO layer, the buffer layer having a resistivity of at least about 10 mohm-cm.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.